code: def test_overlay_integer_indexing(self):
      overlay = NdOverlay(
          list(enumerate([self.view1, self.view2, self.view3]))
      )
      self.assertEqual(overlay[0], self.view1)
      self.assertEqual(overlay[1], self.view2)
      self.assertEqual(overlay[2], self.view3)
      try:
          overlay[3]
          raise AssertionError("Index should be out of range.")
      except KeyError:
          pass
  
file_path: holoviews/holoviews/tests/core/test_layers.py
imports: import unittest
  import numpy
  from holoviews import Element, NdOverlay
label_desc: Use image node_id 3 for calling the OverlayTest obj's underlying member method code with example usage: obj.test_overlay_integer_indexing() without return types